Remove duplicates and leave one document with the most difficultyrating

remove_dups.js

db.beatmaps.aggregate([
    {
        "$group": {
            "_id": "$beatmapset_id",
            "count": { "$sum": 1 },
            "uniqueIds": { "$addToSet": "$_id" },
            "maxRating": { "$max": "$difficultyrating" }
        }
    },
    { 
        "$match": { 
            "count": { "$gte": 2 } 
        } 
    },
    { 
        "$sort" : { "count" : -1 } 
    }
]);

var pipeline = [
        {
            "$group": {
                "_id": "$beatmapset_id",
                "count": { "$sum": 1 },
                "uniqueIds": { "$addToSet": "$_id" },
                "maxRating": { "$max": "$difficultyrating" }
            }
        },
        { 
            "$match": { 
                "count": { "$gte": 2 } 
            } 
        },
        { 
            "$sort" : { "count" : -1 } 
        }
    ],
    counter = 0,
    bulk = db.beatmaps.initializeOrderedBulkOp();

db.beatmaps.aggregate(pipeline).forEach(function(doc) {
    bulk.find({ 
        "_id": { "$in": doc.uniqueIds },
        "difficultyrating": { "$lt": doc.maxRating }    
    }).remove();

    counter++;
    if ( counter % 500 == 0 ) {
        // Execute per 500 operations and re-init.
        bulk.execute(); 
        bulk = db.beatmaps.initializeOrderedBulkOp(); 
    }
});

// Catch any under or over the 500's and clean up queues
if (count % 500 != 0)
    bulk.execute();